Refrigerating machines such as refrigerators, car air-conditioners, room air-conditioners, and automatic vending machines have a compressor for circulating a refrigerant in a refrigeration cycle. The compressor is charged with a refrigerating machine oil for lubricating a sliding part. The refrigerating machine oil is used in the refrigeration cycle in the coexistence of a refrigerant at a wide range of temperatures from low to high temperatures and, therefore, the refrigerating machine oil is required to have various properties such as: lubricity, and thermal and chemical stability, in the presence of the refrigerant; compatibility with the refrigerant; and low-temperature properties. Such properties of a refrigerating machine oil may show unpredictable behaviors depending on the kind of the coexisting refrigerant; thus, development of a refrigerating machine oil is necessary for each refrigerant.
For example, Patent Literature 1 discloses a polyolester oil and polyvinyl ether oil having predetermined properties as refrigerating machine oils that improve wear resistance in the presence of a difluoromethane refrigerant.